1. Field of the Invention
The present invention relates to a liquid crystal panel and a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device can be thinner and lighter than a cathode ray tube (CRT, usually called a Braun tube) that was the leading display device in the twentieth century. In addition, along with the development of technologies to improve image quality such as a development of viewing angle expansion technology or a development of moving image technology, applications and markets of liquid crystal display devices have been expanded to include a monitor for a desktop personal computer, monitors for desktop publishing (DTP) and computer-aided design (CAD), and a television set.
In those applications, there is a strong demand for good color reproducibility and high contrast ratio. In particular, a display that can express dark black color without light leakage is a condition for high image quality. This is a necessary specification for expressing low gradation without blocked up shadows when a darkish image such as a movie is viewed in a dark room with reduced lighting or for expressing delicate color tone of a costume having a neutral tint with low saturation in an image of a performing arts such as opera.
Further, when a plurality of people view a large-screen liquid crystal display device, not only image quality when viewed from the direction vertical to the screen but also image quality when viewed from oblique directions is important. In particular, because light leakage in an oblique direction in a black display causes a substantial damage to the image display quality, it is necessary to take a measure to reduce the light leakage in the oblique direction.
The light leakage in the oblique direction in a black display of the liquid crystal display device is generated by (1) viewing angle dependence of a polarizing plate, (2) partial polarization cancellation due to a liquid crystal panel member inside the polarizing plate disposed orthogonally, (3) viewing angle dependence of a liquid crystal layer itself, and the like. As to an in-plane switching liquid crystal display device, the above-mentioned items (1) and (2) are main factors of the light leakage in the oblique direction in a black display. As to a vertically aligned liquid crystal display device, the above-mentioned items (1), (2), and (3) are main factors of the same.
Further, Japanese Patent No. 3526830 discloses optimal characteristics of a phase difference plate for reducing viewing angle dependence of the polarizing plate by theoretically determining birefringence characteristics for equalizing a polarized state of light that has passed through a polarizer in the case of oblique incidence to the polarized state in the case of perpendicular incidence. In addition, concerning the partial polarization cancellation due to a liquid crystal panel member, a technology of reducing light scattering by pigment particles of a color filter or the liquid crystal layer is reported as a technology for improving a contrast ratio in the vertical direction (front direction) in general. In addition, Japanese Patent No. 3863446 discloses optimal characteristics of a biaxial phase difference plate that compensates for retardation in the thickness direction of the vertically aligned liquid crystal layer and viewing angle characteristics of the polarizer. Note that, there are other prior art documents related to the present invention, which include Japanese Patent Application Laid-open No. 2000-137116, Japanese Patent Application Laid-open No. 2000-91734, Japanese Patent Application Laid-open No. 2001-235622, Japanese Patent Application Laid-open No. 2004-163452, and Japanese Patent Application Laid-open No. 2008-107766.